Which THREE statements about /etc/hosts on a glibc system are correct? (Choose three.)
LPIC-1 Exam 102-500, objective 109. Networking fundamentals hard
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Choose 3.
Correct A line starts with an IP address, followed by the canonical hostname and then any number of aliases, all separated by whitespace.
Correct. That is the field order of the file: address first, canonical name second, aliases after it.
Correct Whether the file is consulted at all, and whether it wins over DNS, is decided by the hosts line of /etc/nsswitch.conf.
Correct. The file is reached through the files NSS source, and its position on that line relative to dns or resolve decides precedence.
Correct IPv6 addresses may be used, so an entry such as `::1 localhost ip6-localhost` is valid.
Correct. The address field takes either family; a standard file ships with both 127.0.0.1 and ::1 entries.
Not correct dig consults the file before sending a query, so an entry there changes what dig reports.
Wrong. dig is a DNS client and talks only to name servers. It never reads /etc/hosts, which is why dig and ping can disagree about a name.
Not correct Comments are introduced by a semicolon, matching DNS zone file syntax.
Wrong. In /etc/hosts a comment runs from a # to the end of the line. The semicolon convention belongs to zone files, not to this one.
Not correct An edit only takes effect once systemd-resolved or nscd has been restarted.
Wrong. The file is read on demand during lookups, so an edit applies to the next resolution. A caching layer may hold an older answer, but no restart is required for the file itself.
Why
/etc/hosts is a flat table of address, canonical name and optional aliases, one entry per line, with # starting a comment and both address families permitted. It is reached only through the files source of the hosts database in /etc/nsswitch.conf, so its authority depends entirely on where files sits on that line. The distinction worth carrying is that NSS-based lookups (getaddrinfo, getent, ordinary applications) see the file, while DNS clients such as dig and host do not.
Where this comes from
- Cited
- manual page hosts(5)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 109 and space the ones you get wrong.
More questions on this objective
- A subnet is defined as 192.168.10.0/26. How many addresses in it can actually be assigned to hosts? machine-checked
- A host is configured with the address 172.20.35.77/20. What is the network address of its subnet? machine-checked
- In IPv6, which address is the loopback address, equivalent in role to 127.0.0.1 in IPv4? machine-checked
- Which is the correct fully compressed form of the IPv6 address 2001:0db8:0000:0000:0000:ff00:0042:8329? machine-checked
- Which pairing of a service with its default port number is correct? machine-checked
- DNS normally uses UDP port 53. In which situation does a DNS client or server fall back to TCP on port 53? machine-checked